This invention relates generally to leak detection. More specifically the invention relates to leak detection for gas cylinders and valves.
In the use of packaged gases, conventional practice in many industrial applications has been to utilize high-pressure cylinders for storage, transport and dispensing of a wide variety of gases. In these applications, gas is contained in the cylinder in a compressed state, to maximize the inventory of the gas available for dispensing and ultimate use.
Since pressure of such compressed gases typically greatly exceeds atmospheric pressure, structural integrity of the gas package is critical to safety in the use of such packages, since any leakage from a high-pressure container will quickly spread to the surrounding environment of the container. Where the gas is hazardous, e.g., toxic, pyrophoric, or otherwise detrimental to health or safety of persons exposed to same, or deleterious to the environment or operability of facilities in the vicinity of the container, structural integrity of the gas-containment package is vitally important to user acceptance and commercial success of the package.
For these reasons, it has been common practice in the gas industry to leak test gas packages, such as conventional high-pressure cylinders, e.g., by methods in which the sealed high-pressure vessel, or a portion thereof having joints or seams susceptible to leakage, is submerged in or contacted with liquid to determine the presence of leaking gas by bubble formation, or by methods using detectors that are sensitive to the gas of interest, such as leak-testing the sealed vessels with “gas sniffer” devices coupled to chemical analyzers.
In view of the safety and reliability issues involving packages of high-pressure gases in the semiconductor industry, efforts have been made in recent years to significantly increase the safety of gas packaging. This effort has produced sorbent-based fluid storage and delivery systems, such as those described in U.S. Pat. No. 5,518,528, in which gas is adsorbed and stored on a physical adsorbent in a fluid storage and dispensing vessel and is desorbed from the adsorbent and discharged from the vessel under dispensing conditions. In these systems, the gas can be stored and dispensed at sub-atmospheric pressure levels, typically below about 700 ton. Such physical adsorbent-based systems are commercially available from ATMI, Inc. (Danbury, Conn., USA) and Matheson Tri-Gas, Inc. (Parsippany, N.J., USA) under the trademarks SDS and SAGE.
More recently, an enhanced safety fluid storage and dispensing system has been developed, in which fluid is contained in a vessel having a fluid pressure regulator in the interior volume of the vessel. Such arrangement is effective to permit fluid to be stored at high pressures, with the regulator being operative to discharge fluid from the vessel only when it sees a downstream pressure that is below the set point of the regulator. Such internally disposed regulator systems are more fully described in U.S. Pat. Nos. 6,101,816 and 6,089,027, and are commercially available from ATMI, Inc. (Danbury, Conn., USA) under the trademark VAC.
Despite these developments of safer gas packaging, it remains critical for gas packages to be fabricated without the occurrence of, or potential for, gas leakage at seams, joints and fittings. Toward such objective, safe, effective and reproducible leak-testing is vital to verify that pressurized gas vessels are leak-free in character, and this is particularly true in the semiconductor manufacturing industry, where reagent gases may be extremely toxic and even lethal at low concentrations, in some instances as low as parts-per-million or even parts-per-billion.
In consequence, the art continues to seek improvements in systems and techniques for determining the presence of leaks in vessels employed for packaging of gases, and in verifying the suitability of such vessels for extended leak-free service.